The present invention relates to a keyswitch structure for computer keyboard, especially to a keyswitch structure using metal balance rod for larger keycap.
Keyboards are popular input device for people in information processing unit such as computer and apparatus requiring frequent input such as cash register. Therefore, the keyboards are under extensive research to provide better performance such as good tactile feel, movement, sound and balance.
Conventional keyswitches with lever mechanism (scissors type keyswitch) are extensively used in keyboard for notebook computer. However, the keyswitch with larger keycap (such as double cap size or triple cap size) has the problem of tilt key cap because larger size and unbalance force (force not at the center of the keycap). The keyswitch with larger key cap are liable to malfunction or the data cannot be exactly input. To overcome this problem, a resilient metal balance rod is provided between the cap and the base of the keyswitch.
FIGS. 1, 2 and 3 show a conventional keyswitch with a keycap 10a, a first lever 11a, a second lever 12a, a base 13a and a balance rod 14a, wherein the first lever 11a and the second lever 12a are cross to each other. The first lever 11a has a pivotal shaft 15a pivotally connected to a pivotal stage 17a on the base 13a and the second lever 12a has a pivotal shaft 16a pivotally connected to a pivotal stage 18a on the base 13a, respectively. Each of the first lever 11a and the second lever 12 has a top end connected to a bottom face of the keycap 10a, whereby the first lever 11a and the second lever 12 form a lever mechanism.
The first lever 11a of the lever mechanism has a bump 19a placed at a lower center end thereof and the base 13a has a flange 20a on top face thereof and corresponding to the bump 19a. The bump 19a is in contact with and clamped by the flange 20a during downward stroke of the keycap 10a. 
The balance rod 14a is a metal rod of U shape and has a center rod section 21a pivotally connected to bottom of the keycap 10a and two lateral rod sections 22a. Each of the lateral rod sections 22a is pivotally connected to a rounded holes 24a of in a groove 23a of the base 13a. The rounded holes 24a extends along horizontal direction and is higher than a top face of the base 13a. The provision of the balance rod 14a enables a force exerting on the keycap 10a being concentrated at center of the keycap 10a such that the keycap 10a can be stably moved upward and downward as shown in FIGS. 2 and 3.
A rubber dome 25a is placed between the keycap 10a and the base 13a. When the keycap 10a is guided by the lever mechanism for vertical up and down movement, the rubber dome 25a below the keycap 10a will detach from. or touch a flexible circuit board 26a on the base 13a and a switch on the flexible circuit board 26a is turned off or on.
However, to allow a rotational movement of the balance rod 14a, a larger contact allowance is provided for the rounded holes 24a through which the lateral rod sections 22a passes, as shown in FIG. 2A and FIG. 3A. The larger contact allowance is the source of noise in current keyboard for notebook computer. Moreover, if the lateral rod section 22a has larger contact area with the rounded hole 24a, noise is also liable to occur.
It is an object of the present invention to provide a keyswitch structure for keyboard of notebook computer, wherein the keyswitch structure has reduced gap between the balance rod and the base, and reduced noise.
It is another object of the present invention to provide a keyswitch structure for keyboard of notebook computer, wherein the keyswitch has a hook atop a groove thereof to provide more restriction on the stroke thereof.
To achieve above object, the present invention provides a keyswitch structure for keyboard of notebook computer comprising a keycap, a first lever, a second lever, a base and a balance rod. The base has two holed groove lugs. Each lug has a rectangular hole. The rectangular hole has an accommodating section on a bottom side thereof which lowers relative to a top face of the base. The balance rod has a center rod section and two lateral rod sections vertically extending from two ends of the center rod section. The center rod section is pivotally connected to the connection stage of the keycap and the two lateral rod sections pass through and are enclosed by the rectangular holes. The keyswitch structure has a reduced gap between the balance rod and the base and the keyswitch structure has reduced noise.
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings, which are given by way of illustration only, and thus are not limitative of the present invention, and in which: